OK so I'm finishing off my first railroad spike knife, and I know that the metal is to soft to hold an edge for long. Any hints on how to temper the edge with a propane torch?

Don't temper just harden. Still a fancy letter opener but a wee bit better.
Finnr

makea soulition of salt water...cold and "harden" bout the best ya can do for that steel

Thanks guys.

Don't know if a propane torch will be enough, you need to heat the blade till it's glowing, slightly above the temperature where a magnet will lose it's attraction to it and then quench in cold salt water. This will harden it. Probably not need much tempering but if you want to I would ssuggest 325 deg F in a kitchen oven for 1 hour.